Presensitized plate

Abstract

A thermal negative type presensitized plate provided with an image recording layer hardened by infrared rays on an aluminum support, wherein the aluminum support has on the surface thereof, a grain shape with a structure in which a grained structure with medium undulation with a specified aperture diameter and a grained structure with small undulation with a specified aperture diameter are superimposed. For the presensitized plate, contact characteristics between the image recording layer and the support and scum resistance on a non-image area are kept compatible with each other at a high level, a thermal diffusion depression effect by which an energy generated by exposure can be efficiently used to form an image is excellent, and sensitivity is high.

Description

[0001] 1. Field of the Invention[0002] The present invention relates to a support suitable for a lithographic printing plate having a photosensitive and / or thermosensitive image recording layer and a presensitized plate using the support for a lithographic printing plate. More particularly, the present invention relates to a support for a lithographic printing plate suitable for the formation of a thermal negative type recording layer and a presensitized plate using the support for a lithographic printing plate.[0003] 2. Description of the Related Art[0004] In recent years, with the development of an imaging technology, attention has been drawn to a direct plate making technology where a narrowed laser beam is scanned on a printing plate to directly form a character manuscript, an image manuscript or the like on the printing plate without using a film manuscript.[0005] In a so-called thermal negative type lithographic printing plate where a photothermal conversion takes place in a r...

AI Technical Summary

Benefits of technology

[0016] Particularly, the present invention aims to provide a high-sensitivity thermal negative type presensitized plate and a support for a lithographic printing plate used for the presensitized plate where the contact characteristics between the image recording layer and the support and the scum resistance on the non-image area are kept compatible with each other at a high level, and a thermal diffusion depression effect by which energy generated by exposure can be efficiently used to form an image is excellent.

[0017] In addition, in the present invention, the contact characteristics between the image recording layer and the support is excellent and the sensitivity can be improved since the hardening reaction of the image recording layer adequately progresses by increasing the thermal diffusion depression effect. Furthermore, the scum resistance of the non-image area can be improved by the hydrophilicity of the support surface.

[0018] The inventors have thought that the contact characteristics between the image recording layer and the support, and the improvement of the sensitivity can be achieved by improving the efficiency of the image formation reaction by heat generated from the photothermal conversion agents such as infrared absorbents. More concretely, the inventors have thought that the contact characteristics and the improvement of the sensitivity can be achieved by improving "the thermal diffusion depression effect by which the energy generated by exposure can be efficiently used to form an image". Consequently, the inventors have found that the thermal diffusion depression effect can be increased by variously reviewing ways to set the structure of profile irregularities on the surface of the support for a lithographic printing plate at a specified shape.

Problems solved by technology

In a so-called thermal negative type lithographic printing plate where a photothermal conversion takes place in a recording layer and a negative image is formed by lowering an alkali-solubility of the recording layer by heat generated, which is the representative aspect of the direct plate making technology, since heat is generated by photothermal conversion agents such as infrared absorbent in the recording layer by irradiating a laser beam and an image formation reaction is triggered by heat, the following problems occur if an image formation reaction by heat is not sufficient.

Then, since the hardening reactivity of the recording layer particularly at the interface between the support and the recording layer is not sufficient, the contact characteristics of an image area with the support is not sufficient, thus press life occasionally deteriorates.

Thus, an inadequate inking may occur and the deterioration of press life may be caused by the problem of the insufficient hardening reaction of the recording layer at the interface.

However, since special equipment is required and the process is complicated, it is the status quo that the industry hopes to have a negative type lithographic printing plate capable of forming a better image dispensing with performing a post-heat treatment like this.

Furthermore, in the thermal negative type recording layer where an image is formed by a laser exposure, the following problems exist.

Since the surface of the support is exposed and becomes a hydrophilic area when the unhardened recording layer of a non-exposed area (a non-image area) is removed by a developer, scum tends to develop easily at the non-image area due to the attachment of an undesired ink-receptive ink at the time of printing if hydrophilicity of the support surface is not adequate.

In addition, there is also a problem that if a developer exhausts and the sensitivity of the solution shown by the conductivity lowers, the solubility of the recording layer deteriorates and a residual layer is generated, and scum tends to develop easily at the non-image area.

However, each trial cannot reach a sufficiently satisfactory level.

On the other hand, if the average aperture diameter of the pit of the grained structure with small undulation exceeds 0.2 .mu.m, the aforementioned anchoring effect by the grained structure with medium undulation may not be obtained since the grained structure with medium undulation is broken.

If the average wavelength of the grained structure with large undulation exceeds 100 .mu.m, inspectability of the printing plate may be impaired since the exposed non-image areas appear dazzling after exposure and development.

If TP exceeds 3 msec, particularly when nitric acid electrolyte is used, an aluminum plate is easily affected by trace components in an electrolyte represented by ammonium ion or the like that spontaneously increase in electrochemical graining treatment, thus the even graining is not easily performed.

As a result, scum resistance is likely to deteriorate when a lithographic printing plate is prepared.

Further, insufficient adhesion of the support to the image recording layer and uneven thickness of the recording layer applied on the support may often reduce the thermal diffusion depression effect, leading to inferior sensitivity.

If it is lower than 50 Hz, the carbon electrode of a main electrode is easily dissolved, and if it is higher than 70 Hz, it is easily affected by the components of inductance in a power supply circuit, thus an electric power cost increases.

If cathodic amount of electricity is less than 3 C / dm.sup.2, an amount of attached smut may be insufficient, and 2 if it exceeds 80 C / dm.sup.2, an amount of attached smut may be too excessive.

If an amount of etching exceeds that range, it is less economical.

In addition, dirt may deteriorate during printing.

If it is more than 5 g / m.sup.2, a large quantity of electricity is needed for the production, which is economically disadvantageous.

If treatment time is shorter than 1 hour, an effect of soaking treatment may be insufficient.

Attachment of a plate to the plate cylinder of a printing machine, however, deteriorates if the elasticity is enhanced.

Since a scratch on the surface of an aluminum plate may become a defect when processed into a support for a lithographic printing plate, it is necessary to suppress as much as possible the generation of a scratch at a stage before a surface treatment process to produce a support for a lithographic printing plate is performed.

Although a compound with large molecular weight or a compound with high hydrophobicity is excellent in sensitivity and layer strength, there may be some undesirable cases in developing speed and deposition in the developer.

However, if the compound ratio is too excessive, undesirable phase separation may occur, a problem in a manufacturing process (for example, a defect in manufacturing attributable to the transfer of the recording layer component and adhesion) caused by the adhesiveness of the image recording layer may occur or a deposition may occur from the developer or the like.

If the content is less than 20 wt %, the strength of the image area is insufficient when the image area is formed.

If the added amount of a cross-linking agent is less than 5 wt %, the durability of the thermosensitive layer obtained by an image recording material may deteriorate and if it exceeds 80 wt %, stability at the time of storage may lower.

If the thickness is less than 0.01 .mu.m or less, it is difficult to prevent the abrasion marks in image recording layers when the presensitized plate is superimposed for handling.

If the thickness exceeds 8 .mu.m, printing characteristics may deteriorate due to the variation of a printing pressure since the thickness of the backcoat layer varies with its swelling by a chemical used in the periphery of the lithographic printing plate during printing.

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